Field of the Invention
The present application relates to the shimming of a magnetic field produced by a superconducting magnet.
Description of the Prior Art
Superconducting magnets are used to generate the homogeneous background fields required for magnetic resonance imaging (MRI). Such superconducting magnets need to be cooled to cryogenic temperatures, and so are located within cryostats. They are required to produce a magnetic field within an imaging region which is homogeneous to within a few parts-per-million. To achieve such homogeneity, shimming is required. Shimming involves the adjustment of the magnetic field generated by the bare magnet, typically by placing passive shims—typically ferromagnetic pieces such as plates of steel—between superconducting coils and the imaging region, or providing active shims—typically electromagnetic shim coils which carry a current adapted to correct inhomogeneity in the magnetic field.